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1) describe the data needed for estimating the regulation of alternator by the potier method. Describe how regulation is determined for different power factor.

2) Determine the synchronous impedance and reactance of an alternator where the given field current generates an armature current of 200 A on short circuit and a generated E.M.F of 50 V on open circuit. The armature resistance is 0.1 ohm. To what induced voltage should the alternator be excited if it is to deliver the load of 100 A at a pf of 0.8 lagging, with a terminal voltage of 200 V.

3) Describe the effect of varying the excitation upon the armature current and power factor of the synchronous motor for a constant output with the help of phasor diagram.

4) a) A 500, 1 Phase synchronous motor provides a net output mechanical power of 7.46 KW and operates at the 0.9 pf lagging. Its effective resistance is 0.8 ohm. If iron and friction losses are 500 W and excitation losses are 800 W, determine the armature current. Find the commercial efficiency.

b) A 75 KW,3 phase star connected ,50 Hz , 440v cylindrical rotor synchronous motor operates at rated condition with 0.8 pf leading. The motor efficiency excluding field and stator losses, is 95% and Xs =2.5 ohm. Find:

i) Mechanical power developed

ii) Armature current

iii) Back e.m.f

iv) Power angle

v) Maximum or pull out torque of the motor.

Electrical & Electronics, Engineering

  • Category:- Electrical & Electronics
  • Reference No.:- M913269

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